A metazoan-specific C-terminal motif in EXC-4 and G?-Rho/Rac signaling regulate cell outgrowth during tubulogenesis in C. elegans

Chloride intracellular channels (CLICs) are conserved proteins for which the cellular and molecular functions remain mysterious. An important insight into CLIC function came from the discovery that Caenorhabditis elegans EXC-4/CLIC regulates morphogenesis of the excretory canal (ExCa) cell, a single-cell tube. Subsequent work showed that mammalian CLICs regulate vascular development and angiogenesis, and human CLIC1 can rescue exc-4 mutants, suggesting conserved function in biological tube formation (tubulogenesis) and maintenance. However, the cell behaviors and signaling pathways regulated by EXC-4/CLICs during tubulogenesis in vivo remain largely unknown. We report a new exc-4 mutation, affecting a C-terminal residue conserved in virtually all metazoan CLICs, that reveals a specific role for EXC-4 in ExCa outgrowth. Cell culture studies suggest a function for CLICs in heterotrimeric G protein (G alpha/beta/gamma)-Rho/Rac signaling, and Rho-family GTPases are common regulators of cell outgrowth. Using our new exc-4 mutant, we describe a previously unknown function for G alpha-encoding genes (gpa-12/G alpha 12/13, gpa-7/G alpha i, egl-30/G alpha q and gsa-1/G alpha s), ced-10/Rac and mig-2/RhoG in EXC-4-mediated ExCa outgrowth. Our results demonstrate that EXC-4/CLICs are primordial players in G alpha-Rho/ Rac-signaling, a pathway that is crucial for tubulogenesis in C. elegans and in vascular development.

Automated summary

Chloride intracellular channels (CLICs) are a group of conserved proteins with unknown cellular and molecular functions. Studies on nematodes and mammals have shown that CLICs play roles in regulating cell morphogenesis and vascular development. However, the specific cell behaviors and signaling pathways regulated by CLICs during tubulogenesis in vivo are still unclear.